1. Field of the Invention
The present invention relates to a small generator apparatus for a domestic or household use cogeneration system which has an interconnection function arranged connectable to a power system.
2. Description of the Related Art
As the demand for global environmental protection has broadly been increased, cogeneration systems and dispersion-type power supply systems are now focused for domestic use power generator systems. Those cogeneration systems and power supply systems are interconnected with a commercial power supply system for gaining the operational efficiency. For example, disclosed in Japanese Patent Laid-open Publication (Heisei) 8-182192 is a system which feeds a load with power from both the commercial power supply system and a domestic use generator. More particularly, as the voltage at an output terminal of the generator is set to a level higher than the commercial power supply voltage, it can be consumed prior to the commercial power supply voltage.
In such a conventional generator apparatus, the output of the generator is used as a controlling power supply for controlling the operation of an engine for power generation and the action of an inverter which converts a DC output of the generator into an AC output.
The power output serving as the controlling power supply is merely a portion of the output of the generator. In case that a small generator in a small-output generator system is driven by a gasoline engine or a gas engine for producing an output of 1 kw to 2 kw, the power consumption for controlling the power supply may be a large portion of the output of the generator. As a result, the influence of a switching regulator as a load for the controlling power supply will appear in the form of a waveform distortion of the output of the system which is not negligible.
FIG. 3 is a schematic diagram of a conventional household generator system. A generator 100 is connected to a commercial power supply system 110 while a controlling power supply 120 for controlling the operation of the household generator system is connected to both the generator 100 and the commercial power supply system 110. The controlling power supply 120 supplies each load 130, such as an electric component for the engine or an inverter in the generator 100, with control power.
FIGS. 4A-4C are diagrams showing the waveforms of various components in the generator system. The output current A of the household generator 100 is a sine wave having no distortion (as shown in FIG. 4A). The input current B of the controlling power supply 120 includes harmonic components and is not a sine wave (as show in FIG. 4B). As a result, the current C fed against the stream of the commercial power supply system has a composite waveform deformed by superimposing the distorted sine wave current B over the normal sine wave current A (as shown in FIG. 4C). As it is desired that the current fed in reverse to the commercial power supply system is a normal sine wave including no harmonics, its distortion components have to be eliminated.
The present invention has been developed in view of the foregoing drawback and its object is to provide a generator apparatus of which the quality of the power output is free from being affected by an output of a generator transferred to a controlling power supply.
As a first feature of the present invention, a generator apparatus having a generator driven by an engine and an inverter for converting an alternating current of the output of the generator into a direct current and driving an inverter circuit to convert the direct current into an alternating current of a predetermined frequency, the inverter connected at its output to a power supply system, comprising a controlling power supply for controlling the engine and the inverter, a first power supply link for rectifying and supplying to the controlling power supply a level of electricity received from the interface between the inverter and the power supply system while the engine remains not actuated, and a second power supply link for supplying the controlling power supply with a level of electricity received from the input of the inverter circuit when the engine has been started, wherein the switching from the first power supply link to the second power supply link is automatically carried out when the voltage at the input of the inverter circuit is increased to a target level.
According to the first feature, as the controlling power supply is supplied with the power at the input of the inverter circuit after the start-up of the engine, it will hardly give adverse effects on the waveform of the output of the inverter circuit. This allows the power supply system to receive a favorable waveform of the current from the output of the inverter circuit.
As a second feature of the present invention, the generator apparatus may be modified wherein the second power supply link is arranged to join with a rectified output of the first power supply link and has a diode provided with its forward direction aligned with the joining direction. According to the second feature, no current is allowed to flow from the first power supply link to the second power supply link and the input of the inverter circuit will hardly become unstable.
As a third feature of the present invention, the generator apparatus may be modified wherein the target level of the voltage at the input of the inverter circuit is set higher than the supply voltage of the first power supply link. According to the third feature, when the voltage at the input of the inverter circuit reaches the target level, the supply can automatically be switched to the second power supply link by the effect of a difference in the voltage between the first and second power supply links.